Oxygen sensor operation theory: when temperature is over 300℃，zirconia can separate
ox ion from of oxygen in the exhaust gas passing through oxygen sensor. If contents of
oxygen in two sides of oxygen sensor are different, a potential difference between two sides
will generate. Measuring the potential difference will obtain the difference of oxygen
contents between two environments (gas air side and exhaust gas side), and then the
information will be sent to ECU. Due to different voltage is corresponding to different
air/fuel ratio, ECU can control fuel injection of injector to regulate gas air/fuel mixture,
making air/fuel mixture approach theoretical value to realize closed loop control. Under
fuel cutting-off and engine full load condition, oxygen sensor does not operate, which is
called open loop.
Volta
e
Rich Lean
excessive air coefficient
Fig 9 Oxygen Sensor and Performance Character Chart
ceramics body 2. Protecting tube 3.outer metal shell of sensor 4. heating resistor
a. signal positive(+) , exposed to air b. signal negative(-) exposed to exhaust gas
The oxygen sensor is heated oxygen sensor, which can enter operating mode much
early. Under normal operating condition, oxygen sensor voltage periodically varies within
0.1～0.9V.
Note: Because lead has inhibitory action to platinum oxidation and leaded gasoline
will make oxygen sensor lose function quickly and deteriorate exhaust gas. Therefore
leaded gasoline is absolutely forbidden.
(7) 3-way catalyst converter
3 way catalyst converter is installed on exhaust, before muffler and can decrease 3
kinds of pollutants’ content in exhaust gas simultaneously: carbon monoxide (CO),
unburned hydrocarbon (HC) and oxide (NOX). When the air/fuel ration of engine is
approaching to theoretical air/fuel ratio, the catalyst efficiency of 3-way catalyst converter
reaches the maximum. When harmful gas under 300℃～800℃ pass through the center of 3
way catalyst converter, it will be catalyzed by precious metal on the ceramic element, taking
oxidizing and reducing reaction, and converts to harmless gas.
To Next Page
Loading...
